Tree of Heaven (Ailanthus), is the preferred host plant for the invasive Spotted Lanternfly, so it is not surprising that the insect is flocking to your tree.
You can learn more about this new pest here: 
https://extension.umd.edu/resource/spotted-lanternfly-home-gardens/
Now that it has arrived, we are finding that Spotted Lanternfly is not as serious as we once thought it might be. Like the Brown Marmorated Stinkbug years ago, it is expected to be a nuisance pest for a while but we are already seeing our birds, insects and wildlife finding them tasty and helping with control.
The areas where they first arrived in Maryland in large numbers are not seeing near as many now.
For that reason we are not recommending any pesticides be applied in home landscapes.

Perhaps one of the best things you can consider doing is have the Tree of Heaven removed. You can't just cut them down as they respond by sending roots out in all directions and you may end up with a plantation of them. There is more info on how to get rid of them (from Penn State) at this link here:
https://extension.umd.edu/resource/tree-heaven/
The timeframe to follow those directions is now through leaf coloring in the fall.


Christine

Thank you for this information.  I have also read about a circle trap to put on the tree that is invested & it traps & kills the fly. Is this worth the effort? My tree is covered with the mature flies & they are excreting the honeydew, but its not in a central area of my yard.  I can kill the tree as recommended.  But when it's dead in the fall & I have it cut down - won't it still have the eggs to worry about destroying?

We have not experimented with circle traps and how effective they are in reducing infestations, but information about their construction and use can be found on the Penn State resources linked on our Spotted Lanternfly web page. Spotted Lanternfly adults can lay eggs on just about anything -- living tree bark, stone, wood decking, house siding (if it's not too smooth a surface), vehicle tires, fabric furniture covers, and so forth. Egg-laying on tree bark isn't limited to Tree of Heaven, so the tree's removal won't necessarily mean that no egg masses are overwintering in the area, whether or not those on that tree are dealt with. Any egg clusters that might be stuck to the Tree of Heaven bark when it's cut down will be destroyed sufficiently well by the wood chipper that the tree will probably be ground-up in by the tree company.

Miri

Thanks for your help

You're welcome.

The fermentation of the honeydew residue they produce (which is mostly sugar-water) is known to be offensively smelly when it's abundant, yes. The insects themselves probably don't smell, and unfermented honeydew also probably doesn't have much of an odor.

Miri

Spotted Lanternfly is a species of planthopper, not a moth, and all life stages, not just the adults, would be vulnerable to topical insecticide sprays. We do not recommend the use of any home remedy for these or other insect issues (the linked page provides some reasons why they are not a good idea).

Pesticides like EPA-registered products using ingredients like horticultural oil (neem oil being one type in this group) or insecticidal soap (which is not the same as household soaps or detergents) can work if they are able to directly coat the insects with the spray. Spray residues that insects crawl over later will not have any impact on them. These sprays can also injure or kill any other insect they come into direct contact with, so make sure only lanternflies are being sprayed if you decide to use them. Follow all label directions, which tends to include a warning about using them while temperatures are above 85 degrees, as then plant damage might occur (especially on foliage). As noted on the Spotted Lanternfly web page that we linked to earlier: "Neem oil and insecticidal soap have a short period of residual activity and would need to be re-applied at intervals recommended on the product label." Therefore, as more lanternflies enter the area over time, you may need to re-treat several times until they are killed by frost in autumn.

Miri

Thank you.

I have another question.   My heavily infested tree is covered with smelly honeydew from the lanternflies.  I am having a big outside party next week.
Is there anything I can do to get rid of or minimize the foul order?  Would power washing it off of the tree trunk at least dilute the honeydew fermenting smell?

Hosing it down with plain water is probably the most practical approach, though we don't have any study data or personal experience to recommend any other techniques.

Miri